package lion.common;

import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

/**
 * 42位的时间前缀+10位的节点标识+12位的sequence避免并发的数字（12位不够用时强制得到新的时间前缀）
 * <p>
 * <b>对系统时间的依赖性非常强，需要关闭ntp的时间同步功能，或者当检测到ntp时间调整后，拒绝分配id。
 * 
 * @author sumory.wu
 * @date 2012-2-26 下午6:40:28
 */
public class IdWorker {
	private final static Logger logger = LoggerFactory.getLogger(IdWorker.class);

	private final long workerId;
	private final long snsEpoch = 1330328109047L;// 起始标记点，作为基准
	private long sequence = 0L;// 0，并发控制
	private final long workerIdBits = 1L;//10L 只允许workid的范围为：0-1023
	private final long maxWorkerId = -1L ^ -1L << this.workerIdBits;// 1023,1111111111,10位
	private final long sequenceBits = 12L;// sequence值控制在0-4095

	private final long workerIdShift = this.sequenceBits;// 12
	private final long timestampLeftShift = this.sequenceBits + this.workerIdBits;// 22
	private final long sequenceMask = -1L ^ -1L << this.sequenceBits;// 4095,111111111111,12位

	private long lastTimestamp = -1L;

	public IdWorker(long workerId) {
		super();
		if (workerId > this.maxWorkerId || workerId < 0) {// workid <
															// 1024[10位：2的10次方]
			throw new IllegalArgumentException(
					String.format("worker Id can't be greater than %d or less than 0", this.maxWorkerId));
		}
		this.workerId = workerId;
	}

	public synchronized long nextId() {
		long timestamp = this.timeGen();
		if (this.lastTimestamp == timestamp) {// 如果上一个timestamp与新产生的相等，则sequence加一(0-4095循环)，下次再使用时sequence是新值
			// System.out.println("lastTimeStamp:" + lastTimestamp);
			this.sequence = this.sequence + 1 & this.sequenceMask;
			if (this.sequence == 0) {
				timestamp = this.tilNextMillis(this.lastTimestamp);// 重新生成timestamp
			}
		} else {
			this.sequence = 0;
		}
		if (timestamp < this.lastTimestamp) {
			logger.error(String.format("Clock moved backwards.Refusing to generate id for %d milliseconds",
					(this.lastTimestamp - timestamp)));
		}

		this.lastTimestamp = timestamp;
		// 生成的timestamp
		return timestamp - this.snsEpoch << this.timestampLeftShift | this.workerId << this.workerIdShift
				| this.sequence;
	}

	/**
	 * 保证返回的毫秒数在参数之后
	 * 
	 * @param lastTimestamp
	 * @return
	 */
	private long tilNextMillis(long lastTimestamp) {
		long timestamp = this.timeGen();
		while (timestamp <= lastTimestamp) {
			timestamp = this.timeGen();
		}
		return timestamp;
	}

	/**
	 * 获得系统当前毫秒数
	 * 
	 * @return
	 */
	private long timeGen() {
		return System.currentTimeMillis();
	}

	public static void main(String[] args) {
		IdWorker iw1 = new IdWorker(1);
	}

}
